Homocysteine (HCy) is a small sulphur-containing alpha amino acid not used in protein synthesis but present in cells and extracellular fluid in low concentrations, e.g. typically about 10 μM in adult human blood plasma. Elevated plasma HCy levels have been associated with folate or vitamin B deficiency and with cardiovascular disease. There is thus significant clinical interest in assaying for HCy in plasma.
One such assay system was developed by Axis-Shield ASA and is available commercially from Abbott Laboratories. In the first six years of sales, over 26 million such HCy assays have been carried out using this system. The Axis-Shield/Abbott HCy assay involves enzymatic conversion of HCy in plasma to S-adenosyl-homocysteine (SAH) and immunoassay detection of the SAH. The Axis-Shield/Abbott HCy assay however is designed to be carried out in clinical laboratories and there remains a need for an HCy assay which is in a format performable at the point-of-care, e.g. in the physician's office, so that the patient need not revisit to learn the outcome of the assay.
An assay performing device capable of use at the point-of-care has recently been developed by Axis-Shield ASA. This is available commercially under the trade mark Afinion and is described for example in WO 02/090995, the contents of which are hereby incorporated by reference. In the Afinion system, a sample (e.g. blood, plasma, urine, etc) is placed in an assay cartridge which contains several wells pre-loaded with the reagents required for the performance of the assay and carries computer-readable information sufficient to enable the device to determine how to perform the assay for the particular sample type and analyte of interest.